The launch appeared to be going smoothly, but some 90 seconds later Nasa, on its livestream, reported that a problem seemed to have occurred with the booster rocket between the first and second stages of separation.

Footage from inside the capsule showed the two men being shaken around at the moment that the fault happened.

Shortly afterwards, Nasa said they were making a "ballistic descent" meaning their capsule descended at a much sharper angle than normal and would have been subjected to greater G-force - the force imposed on a body by rapid acceleration.

The capsule separated from the failing rocket and later deployed parachutes to slow its descent.